I. Field of the Invention
This invention relates generally to processes for forming antioxidants and similar compounds. This invention relates more particularly to improvements in a process for the formation of a trialkyl-tris(3,5-dialkyl-4-hydroxybenzyl)benzene with a sulfuric acid catalyst or a Friedel-Crafts catalyst.
II. Description of the Prior Art
The products formed by the process of the present invention and earlier similar processes have been widely used as antioxidants in food, animal feed, stock chemicals and the like. Such antioxidant use has also proven especially valuable and effective in polymeric materials and rubbers.
The process presently used for production of the above-mentioned antioxidant products comprises two main steps. Such a process is set forth in Rocklin et al, U.S. Pat. No. 3,026,264, which patent is incorporated herein by reference.
A 3,5-dialkyl-4-hydroxybenzyl alcohol precursor is formed by the potassium hydroxide/isopropyl alcohol condensation of dialkylphenol and formaldehyde. After neutralization of the reaction mass with, e.g., acetic acid and isolation of the reaction mass, the product of the first step is reacted with a trialkylbenzene in the presence of a catalyst. The yields from the known process are inconsistent but within the range of about 55-75%.
Various techniques to improve yields have been tried but have proven to be inconsistent at best. Equipment modifications and reaction mass agitation have not resulted in consistently good yields. Thus, any improvement which would reliably yield increased amounts of product and decreased amounts of by-products would be extremely valuable. The demand for the antioxidant products is high, in some cases so great as to justify additional capital expenditure for new plant facilities.
An alternative process has been proposed for the production of the types of antioxidants discussed above. However, that alternative process has also proven to be impractical. Shin, in U.S. Pat. No. 3,925,488, has suggested carrying out the process in a low boiling inert solvent with a sulfonic acid catalyst. Shin suggests that such a process avoids undesirable dealkylation by using a low boiling solvent and minimizes the quantity of catalyst required.
Shin also suggests the gradual addition of formaldehyde to the reaction system of such a process so as to increase the yield. However, the yield increase was not very high. The overall performance and cost-effectiveness of the Shin process have proven to be poor.